Experimental Heat Transfer and Discharge Coefficients for Single Confined Jet Impingement Normal to a Surface at Close Distances

摘要

Heat transfer and flow discharge coefficients for confined jet impingement are being investigated for a single round jet impinging normal to a target surface less than one hole diameter from the jet origin. A search of open literature resulted in the availability of no discharge coefficient information, and limited heat transfer information, especially for the configuration of a confined jet in close surface impingement. The experiment has been conducted for a developing jet and utilizes liquid crystal thermography for heat transfer measurements. Nusselt numbers were obtained for jet Reynolds numbers between 15000 and 30000 with a gap to hole diameter ratio of 0.3 to 3. Discharge coefficient data were obtained for jet Reynolds numbers between 11000 and 59000, with a gap to hole diameter ratio of 0.2 to infinity. The heat transfer data obtained shows a secondary Nusselt number peak and similar trends to those seen in other close surface impingement studies. The data also show a crossover of Nusselt number at increasing radial distance from the jet stagnation point with increasing gap size which could be indicative of ambient air entrainment. The discharge coefficient data obtained show a decrease in discharge coefficient for a decrease in gap size. At constant pressure ratio con-ditions a large decrease in discharge coefficient is observed between pressure ratios of 1.05 and 1.11. The results of this study are applicable to many industrial applications. However, a discussion of close surface impingements applicability to gas turbines has been included, as well as a comparison of the experimental and numerical results.